There has been research into and demonstration of the use of non-radio frequency communications for RPAS flight control.  These include the use of modulated lasers, which have been shown to propagate to considerable distances and would be easily adequate for typical Visual Line of Sight (VLOS) operations.

Modulated lasers can be highly directional and thus less likely to be subject to certain types of interference.  As such they might have security benefits.  Laser safety (especially for eyes) is an important consideration.

Further Reading

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